The technology failure that shut down Nasdaq for more than three hours Thursday exposed a weakness in the plumbing of the market that critics say reflects years of neglect by U.S. exchanges and regulators.

While exchanges have spent hundreds of millions of dollars developing lucrative, direct pipelines and state-of-art computer systems that provide superfast connections to high-speed traders, they have spent relatively little on the system that constantly feeds stock orders and trades to the rest of the market, according...